The destruction of particles has been long associated with high-energy physics and the construction of large-scale particle accelerators. It is perhaps less well-known that in solid state physics, the destruction of particles, or more precisely quasi-particles, takes place on a regular basis in a standard laboratory environment. Quasi-particles are the fundamental excitations of a metal. Simple changes in a sample's environment (e.g. through changes in its temperature, dimensionality or doping level) can alter the spectrum of quasi-particle excitations and thus lead to fundamentally new physics. In my research, I investigate ways in which the quasi-particle description breaks down in a host of exotic new materials known collectively as strongly correlated metals. This family of metals, that include the high-temperature superconductors and colossal magnetoresistance oxides, are not only interesting from a fundamental perspective; they also have huge technological potential.